The present invention relates to scroll apparatus and, more particularly, to scroll apparatus for use in vacuum pumps.
Scroll apparatus is known for operating compressors or vacuum pumps. In both cases the apparatus comprises two scroll members each comprising a flat end plate on which are upstanding strips of uniform width defining a spiral (or scroll) type structure which interact by placing the scroll members substantially co-axially together with the respective spiral type structures inter-engaging and allowing one scroll member to xe2x80x9corbitxe2x80x9d relative to a stationary member.
In this way it is possible to trap a volume of gas between the orbiting scroll member and the fixed scroll member thereby to urge the gas from one end of the respective spirals to the other. In a vacuum pump in particular the gas enters via a pump inlet at the periphery of the scroll members and exits via a pump outlet at the centre of the scroll members.
The orbiting scroll member is caused to xe2x80x9corbitxe2x80x9d by allowing it to inter-engage with bearings positioned eccentrically on a rotating drive shaft which is itself driven by a motor. The orbiting scroll member is constrained from rotating by means such as Oldham couplings or other known means.
In PCT publication W096/26366 there is described a vacuum pump incorporating scroll-type apparatus in which the orbiting scroll member is driven by means of a pump shaft that is centrally located in relation to a stationary body. A mechanism is provided for connecting the orbiting scroll member to the stationary body so that it is supported thereby and controls the circular translational motion of the orbiting scroll member. The mechanism comprises at least one bearing supported by the pump shaft and a metallic bellows for limiting undesirable travel in the circular translation of the orbiting scroll member.
It is an aim of the present invention to provide a vacuum pump of the scroll-type which provides a seal between a vacuum space in the pump from atmosphere where the pump shaft extends through the case and also prevents the orbiting scroll member from rotating.
According to the present invention a vacuum pump of the scroll-type comprises a housing, a first fixed scroll member having an end plate and an involute spiral wrap attached thereto, a second orbital scroll member having an end plate and an involute spiral wrap attached thereto, the scroll members being arranged in the housing such that their respective wraps intermesh so that on orbital movement of the second scroll member relative to the first scroll member a volume of gas will be urged from one end of the wraps to the other end, a shaft for driving the second scroll member and wherein a member is provided which is adapted to separate the vacuum space in the housing from the shaft and also prevent the second scroll member from rotation, said member being made from a polymer material.